1. Technical Field
The present invention relates to a head mounted display.
2. Related Art
There is a known head mounted display (HMD), which is a display worn around user's head for use. A head mounted display, for example, generates image light representing an image by using a liquid crystal display and a light source and guides the generated image light to user's eyes by using a projection system and a light guide plate to allow the user to recognize a virtual image. Further, uncomfortable dazzle and other types of psychological discomfort resulting from a high-luminance object are known to be expressed by discomfort glare, and there are a plurality of known discomfort glare evaluation methods for numerically representing discomfort glare.
JP-A-2008-92481 discloses a dazzle evaluation image and image display. The dazzle evaluation image contains a white rectangular image (white rectangle) against a black background, and the proportion of the area of the white rectangle to the area of the entire evaluation image and the luminance of the white rectangle are changed to identify a threshold that is derived from the relationship between the proportion of the area of the white rectangle and the luminance thereof and corresponds to dazzle that causes the user who recognizes the evaluation image to feel discomfort. The image display compares a display image actually recognized by the user with the threshold to adjust the luminance of the display image. JP-A-2010-58631 discloses a head mounted display that captures an image of a surrounding scene. When the image of the surrounding scene contains a high-luminance object, the head mounted display adjusts the transparency of the surrounding scene recognized by a user to smoothen the illuminance of the transmitted surrounding scene for reduction in discomfort glare.
The image display described in JP-A-2008-92481, however, simply considers the luminance of only an image displayed by the image display but does not consider the illuminance of a surrounding scene recognized by the user and hence has room to reduce discomfort resulting from dazzle that the user feels. The head mounted display described in JP-A-2010-58631 adjusts only the illuminance of the transmitted surrounding scene recognized by the user but it is desired to make the adjustment in consideration of the luminance of image light that the head mounted display allows the user to recognize, in other words, based on the illuminance of the surrounding scene and the luminance of the image light recognized by the user. It is further desired to not only control the illuminance of a surrounding scene and the luminance of an image recognized by the user but also increase visibility of image light recognized by the user.
The following non-patent documents are exemplified as other related art documents: “Discomfort glare in indoor environment,” [online], [searched on Jul. 9, 2013], Internet <http://www.tlt.co.jp/tlt/lighting_design/design/basic/data/26_35.pdf>; IWASAKI ELECTRIC CO., LTD., “Evaluation of discomfort glare,” [online], [searched on Jul. 9, 2013], Internet
<http://www.iwasaki.co.jp/info_lib/tech-data/knowledge/glare/02.html>; and KIM Wonwoo, other two, “Position Index for a Glare Source in the Whole Visual Field,” Journal of Light & Visual Environment, The Illuminating Engineering institute of Japan (general incorporated association), Vol. 83 (2004) No. 11, pp. 847-852.